1. Field of the Invention
The present invention relates to an active matrix-type display device using an electro-optic material such as liquid crystal, and more particularly, to an active matrix-type display device having less data bus lines than those of a normal type.
2. Description of the Related Art
An active matrix-type display device as well as a simple matrix-type display device is thin, and therefore, is often used in various thin display devices of information terminals. Generally, liquid crystal is used as electro-optic material of this device. Compared to the simple matrix-type liquid crystal display device, in this active matrix-type liquid crystal display device, since individual pixel elements are independently driven, the contrast is not reduced based upon the reduction of duty ratio, and the angle of visibility is not reduced, even when the capacity of the display is increased to increase the number of lines. Therefore, the active matrix-type liquid crystal display device enables a color display in the same way as in a cathode ray tube (CRT), and is prevalent in flat display devices.
However, since the active matrix-type liquid crystal display device has a complex configuration and one thin film transistor (TFT) as a switching element is provided for each pixel, a complex manufacturing process is required, and equipment therefor is expensive. Also, the manufacturing yield is low. Further, in the active matrix-type liquid crystal display device, the number of driver ICs increases according to an increase in display abilities, thereby making the active matrix-type liquid crystal display device expensive. Therefore, in order to improve the low manufacturing yield, various types of active matrix-type liquid crystal display devices have been suggested.
One type is a counter-matrix active matrix-type liquid crystal device in which scan bus lines and data bus lines are formed on different substrates, so that intersections of scan bus lines and data bus lines on the same substrate are not used (see: U.S. Pat. Nos. 4,694,287, 4,717,244, 4,678,282).
In other types of devices disclosed in Japanese Unexamined Patent Publication Nos. 62-218987, 3-38689, two neighboring pixel elements are respectively connected to the same data bus line via two independently controlable TFTs, and are driven at time division sequences, thereby reducing the number of the data bus lines. Since the data bus driver is more complex than the scan bus driver, the driver configuration of this device is very simple. However, in the above documents, examples of the counter-matrix active matrix-type liquid crystal device in which the number of data bus lines is reduced are not disclosed.
Further, in the active matrix-type liquid crystal display device, improvement in display quality and duration are also desired. In any type of active matrix-type liquid crystal device, a DC component resulting from parasitic static capacitense and the unipolarity of the address pulses is generated. For example, flickers and residual images may be generated. Particularly, for a stationary image, a burning phenomenon may occur. Also, the life-time of active matrix-type liquid crystal devices may be shortened.
In the Japanese Unexamined Patent Publication No. 53-144297, the active matrix-type display device in which one pixel electrode is connected to two data bus lines via two switching elements is disclosed. The two switching elements are respectively controlled by positive and negative address pulses on the same scan bus line. Two positive and negative address pulses are applied for each scanning frame cycle on the scan bus line and two data signals having the same voltages and opposite polarities to each other are applied to the data bus lines in synchronization with the address pulses. By this, two different switching elements are effected individually for each frame cycle, and the influence of the parasitic static capacity is canceled. Therefore, in this device, the above-mentioned DC component can be reduced, and the above problems associated with display quality and the duration are improved. However, this device has a problem in that the number of data bus lines is increased.
Further, the Japanese Unexamined Patent Publication Nos. 63-96636, 2-212819, 4-14091, 4-14092 and 4-102825 disclosed active matrix-type display devices in which each pixel electrode is connected to the data bus line via two different switching elements respectively conducted by positive and negative address pulses, and these two switching elements are simultaneously or individually effected for each scanning frame, thereby canceling the influence of the parasitic static capacity, and the above problems are improved.